Impassioned Amalgamation: The Dark Angel's Heart
by hayclover
Summary: Despite his demon blood, it is humanity and something more driving Sebastian's wicked passion, but only the Mothers know it. But, as he detains his siblings—with Jace in eternal sleep and Clary seeking revenge—to avoid solitude and to make Clary his own, he learns the truth. With a newfound purity that makes his charms valid and dangerously real, will Clary finally accept him? AU


_I'd like to make it clear that there would be no incest, but it actually depends on how you will come to perceive my alterations. Sebastian says he and Clary belong to each other. Just how valid can that be if his feelings were made acceptable? _

…ooOoo...

_Because I honestly think there is some genuine goodness in the real Jonathan Christopher Morgenstern, and as Magnus Bane said, "Nice, bah. He's gorgeous_..."

**Prologue**

Clary couldn't stop herself from shivering as she passed through the corridors inside the Institute. Sebastian had just fulfilled the promise of his return, and what better way to do it than to bring hell to them? But, instead of flames of fury, what the Lightwoods' home received was a snowstorm.

When she had exited the elevator, the first thing she saw was white ice accumulated everywhere. Chairs and tables here and there were knocked over, clearly gushed by a strong force. The walls that surrounded them were either destroyed by the pressure or decorated with thick bluish white flakes. Some paintings had fallen off while some had gotten frozen like the doors. It was a good thing there was no more wind, but the place was still left cold.

Anxiety overwhelmed her. The coldness had gotten her hands too numb to feel the stele that she struggled to hold on to. She felt like she had just been transported into the last circle of hell as in Dante's Inferno, but worse. She was sure she would find the cruelest of all demons—her brother, not trapped in ice, but instead, ruling it, stronger and freer than he had ever been. Now that he wasn't connected to Jace, Sebastian could do whatever he wanted without the risk of hurting himself.

Jace... The thought of him getting hurt by Sebastian disgusted and horrified her. She knew that after being struck by _Glorious_, Jace had new powers that probably made him stronger and fitter to fight Sebastian. But Sebastian was Sebastian. Valentine's son wouldn't attack unprepared after learning from his last hubris, would he?

She raced across the next hall to get to the staircase, above which was Jace's room, when her numbed arm hit something she didn't care to see. She cursed herself for failing to put the silence rune of all runes. Although the noise she made was not loud, it was enough to stir the Greater Demon that was lurking nearby.

Quickly, she forced her weight through the nearest door that was least frozen, so she could hide. She slammed it shut and leaned against it, her eyes closed and her breath running short.

For a moment, she could hear nothing but the eerie sound of silence.

She shuddered. It was horrible that in spite of the cold weather, the breath that escaped her lungs still felt like it was that of the normal temperate day it had been before she entered the Institute. Though her entire body was freezing, what she observed externally was different from what she felt internally. It was almost like...

"That's it," she told herself, her eyes flashing as she remembered a lesson from class where she was taught that heaven and hell were just states of mind. "A glamour of hell," she said bitterly with a bit of amazement that was far less than the horror she felt afterward. This was how powerful her brother was.

She tried to rip off the image in view layer by layer and frowned. Nothing happened. Perhaps she was wrong.

Shrugging, she turned the doorknob to get out of the room when suddenly, something brisk forced her off her feet. Before she could even scream, her body slammed hard against the wall on the other side of the room, and her head hit a candelabrum.

As if she hadn't suffered enough damage, gravity quickly pulled her back to the ground. She bit her lip. She had no time to fuss over a few bruises when Jace could be in trouble. Massaging her injured head, she staggered towards the door.

It was locked. Her opening rune didn't work either.

Sighing and turning around, she tried to scan the room dimly lit in the color of sunset by the rays that passed through the velvet curtains. She was not alone, yet she could not see any creature that could have attacked her.

Could there be a demon that was invisible? If so, then the only solution she could think of was to strike her stele at random everywhere until luck permits her to hit the demon. It sounded stupid, but it was worth considering. Besides, the room was small and almost empty except for a few candelabra and some statues. Moreover, she had enough training on high jumps to reach the ceiling.

Silently, she prayed that the demon was a stupid one.

…ooOoo…

"Clarissa is back," Sebastian announced, more to himself than to Jace. There was oddly a mixture of amusement and ridicule in the way he spoke her name. He shifted his dark eyes from the walls back on to Jace with a grin, his arms folded. His adoptive little brother stared back at him with eyes of contempt.

Sebastian had made his attack quite easily with the Lightwoods away. With Lilith's blood flowing in him not to mention his last visit there, it wasn't difficult to get through security. A few Silent Brothers got in the way, but his rigorous training overcame them nonetheless. After all, his father had taught him every secret to killing every sort of creature including high-level Nephilims.

In fact, it was Jace who became a bit of a trouble. Slaughtering Jace's mute bodyguards singlehandedly only took him a few seconds; getting the stubborn golden-haired angel unconscious and chained up was the real challenge. As if getting hold of Angel Chains wasn't troublesome enough, he had to fight Jace down without touching Jace's bare skin. His mother said a touch of heavenly fire in any form could harm demons.

Seeing his little brother all tied up against a chair and all obedient satisfied him no more than seeing the Angel bloodstains from where he stabbed the tiny daggers on-one on each limb to completely paralyze Jace, and one near Jace's heart just to get back at what happened in Valentine's cave.

As soon as Jace was under his control, all he needed to wait for was Clary. Then, they would be reunited once more.

"It's a good thing you woke up again. I wouldn't want our beloved Clary to think I've killed you," Sebastian said when he figured Jace had nothing to say about his announcement.

"Beloved," Jace finally replied, "you call her so dearly as if you love her. And if you do as you claim, don't you at least feel the slightest shame on your incestuous lust?"

Sebastian looked at him sheepishly. "Oh please. How am I any different from you back when you thought you were I? You may have fought your impulses at first, but eventually you also surrendered. And Clary accepted you too. How should I be any different?"

Jace blinked in disbelief. "What we had was real. Yours was completely one-sided, and you tried to _rape_ her, your own little _sister_."

Sebastian smirked. "You chastise me like you're an angel, Jace Herondale, but we both know you're not. Even before you thought you were part demon—when you already thought you were me—wasn't there a part of you that yearned to do the same? Except we can't call it rape because you had the advantage of her loving you back. Still, you did _try_ to keep yourself under control, and I must admit even I was touched by your passionate love." He took a few steps towards him and leaned close enough just to whisper in his ear, "Tell me, did you two have a good time then? Because I bet I could have given her a better one."

Jace spat at him.

But before Jace's saliva could touch him, he had already disappeared to a few meters away. "Spitting," he said, looking bored and unimpressed. "How inelegant. I guess one of the things you failed to master from our late father was how to act classy... Or has your love for dear Clarissa gone too far that you have taken to even her crude habits?"

"Look, you're lonely. I get it. If you want me, then take me. At least we have some sort of bond from Valentine. But I don't get why you have to force Clary with you too. Sure, you're blood related, but you know she hates you."

Sebastian's lips seemed to purse a little at Jace's remark, but it was just for a second. Then, he smiled. "What about you, little brother? Do you hate me?"

"Are you asking me with love? Because I don't think you're going to like my answer."

"That's sad. I've always been very fond of you. Lilith always said it was love."

Jace snorted. "Is this a confession? Are you trying to tell me you're bi and you want both Clary and me as your toys? Because I'm telling you now, bro, love and lust are two different things. But I might be softer on you on this if you were not so incapable of love."

Sebastian chuckled. "You flatter yourself. Don't worry. I'm not a freak like that brother of yours who runs around with that warlock," he said. "Anyway, if I didn't love you, then I would have just killed you the moment I caught you."

Jace could feel the Angel heat within him grow hotter as his blood boiled. "Alec is not a freak, and so isn't Magnus. If anyone's a freak, then it's you. You didn't do so because Clary would hate you. And you don't want that because you lust for her."

"My lust can be satisfied anywhere, dear brother. You've seen the way I live. And why would I care that she hates me if I did not love her? If it were just lust, then I could just rape her any time I want."

"Because you also need her to trust you," Jace said in return. "You are nothing but another Valentine, Sebastian. Whatever you do is always just a part of your manipulative scheme. You need us as your tools more than companions."

Sebastian sighed. "I must say it is getting tiring to argue with you, little brother. I liked you better when you were tied to me. You were so much cooler."

"I was under your control. It was like you were enjoying your own company."

"Exactly. I was always more charming than you anyway."

"Try telling that to Clary."

"Oh, she'll come around soon enough. She'll learn that I love her, and she'll learn to love me too. But you, little brother, will be harder to convince now that you're infected with Heaven's Fire."

Jace smirked. "Jealous, are you? Clary finds it hot that I'm on fire. You on the other hand, are nothing but ice cold."

Sebastian brushed a hand against his hair. "Not at all. Fire that is hot, but _not__ hot enough_, usually brings danger whereas ice, no matter how cold can still render a lot of benefits. Fire may give light and hope, but ice gives real beauty and power."

"And yet fire is what melts ice," Jace replied. "You will always be alone. A boy lonely forever all because you refuse to let your pride down."

"I am simply living my own version of our father's legacy. It is my obligation to carry out what he has failed to do."

"And so you will be alone. The price you pay for what you think will be a better race of Shadowhunters will be your solitude. But I suppose it is something you are good at already."

It took a second for Sebastian to appear again inches away from Jace. "You talk so well, little brother," Sebastian said quietly, grabbing Jace's torn shirt to pull the him against the Angel Chains.

Jace cried out in pain as the chains electrified him. Sebastian, grinning, released him. "You think I don't know what you are doing, do you? You're trying to provoke me, so you could find an opening to hurt me. Too bad I'm too smart for you."

Jace's face was still down, but Sebastian thought he saw Jace smile. "Are you?" Jace muttered. The Herondale boy spat hard at him in the face, and this time, saliva really hit his skin.

This time, it was Sebastian who cried out in pain as the saliva burned his skin, and he fell to the ground.

…ooOoo…

About half an hour had past since Clary began swinging her stele at random and leaping into the air almost every other minute but to no avail. It was tiring, but she forced herself to keep going. In her carelessness, she accidentally struck a vase that was heavily covered with snow. It fell to the ground and shattered to pieces.

The sound of ceramic breaking was not a pleasant one. She squinted at the sound, which lasted no more than two seconds but seemed like forever. She sighed. Maryse won't be happy. But it was a good thing she and the rest of the Lightwoods were vacationing in Idris this summer... Except for Jace. Jace chose to stay to keep Clary company since Jocelyn wouldn't let her go with them.

She slumped down and sat on the green carpet under her feet. She knew the Lightwoods wouldn't blame her whatever happened. Still, she felt that any harm that comes upon Jace would be on her.

"Damn it," she muttered under her breath. She rubbed her palms together to get some heat. The weather wasn't getting any better.

She wrapped her arms around her knees and dug her face in to think. She was certain it was just a glamour now that she recalled Sebastian's intention of taking over the Institute with Jace. But how can she remove a glamour so strong and so new to her? A slightly stronger glamour alone required her more effort and guidance to uncover what was beneath it.

_Concentrate_, she told herself, but she couldn't. She didn't know whether it was because of the cold that was getting to her. All thoughts seemed to go back to Jace. She remembered the last time she saw him... It was just hours ago. She had been in his arms as they laid side by side. His chest was pressed against her back, and his face was buried in her hair. Along with the vibration from his heartbeat, she could feel the static-like electric heat she has grown used to now. It added up to the warmth Jace had always given her. Times like this, she thought, such heat could really help. She imagined herself in Jace's arms for warmth.

And then, to Clary's surprise, the warmth started to feel real. The temperature began to rise again. She looked up to find the ice melting. _That's it_, she thought. She mentally started fire in every corner of the room until all the ice started melting. She smiled, looking proud at herself.

She turned her head from left to right, as she surveyed the room. Everything started looking dry and clearer—the walls, the window, the vase she had broken...

She could see everything clearly now—including the demon, twice the size of a refrigerator, with bulging black eyes each as big as a turkey, just beside her.

It didn't move; rather, it was staring at her as if confusedly and in wonder.

She fought the urge to scream, and also the urge to laugh. The demon looked both horrifying and oddly funny. She recognized who it was from one of her Shadowhunter lessons: Stupidas, the Greater Demon. He looked stupid indeed in his clown clothes that made him look like those nasty people who tried to look nice in flashy clothes, but just failed miserably.

Tucked in his ruffs was something big and yellow. At first, she thought it was some kind of demon bow tie. But it suddenly moved and purred. Church. The cat didn't look frightened-just sleepy, but his eyes widened when he saw Clary.

"Don't," Clary ordered at once when he was about to leap towards her. She couldn't help feeling slightly happy when he obeyed; it meant he saw her as family, maybe as part of the Lightwoods. Carefully, he slid his forelimbs back inside the ruffles.

Stupidas, sensing Church's movements, broke off from his gaze. As if deciding that Clary was his foe, he raised his gigantic hammer-like hand to pound her. She quickly dodged it. His fist came down at her and missed again, as she ran quickly around the room until she was far behind him.

To her relief, he was as slow as much as he was stupid. She could plunge her stele into his heart without much effort. But before she could backstab him, he turned around and marched towards her looking like a vexed sumo wrestler.

She quickly jumped high in the air, so he couldn't reach her, and she back flipped over its head. In her descent, she clutched his clothes midway and drove her stele into his heart.

The demon gave out a loud, ugly groan before finally disappearing in ashes.

As her feet touched the ground, Clary fumbled her way to catch Church.

"What were you doing with Stupidas? That was dangerous, you know," she told him, and he purred lazily. "You owe me," she said, putting him down, and he looked like he didn't really care.

She walked towards the door with Church behind her. To her dismay, it was still locked. She sighed. "Jace could be in trouble," she said and looked at the cat. "I hope you know another way out."

Church seemed to nod. As he started walking away, she followed him obediently, grateful just this once that the Lightwoods owned a lazy but nosy pet cat.

…ooOoo…

"Jace!" Clary cried when she finally found Jace.

"Clary," he replied with a weak smile. He was still bleeding here and there, and he just looked a complete mess, Clary thought mournfully, but at least he was alive.

She wanted to hug him, but not before she had removed the daggers that were thrust deep into his muscles, and she had marked some _Iratze_ on him. He was going to thank her, but she had already placed her mouth against his. Her lips were soft as always, but they were wet with tears. He wanted to wipe them off her face and pull her in closer, but he couldn't.

She clung onto him for a few more seconds before she released him. He smiled. "Taking advantage of these chains like your brother?"

She scowled. "I thought I was going to lose you again." She rubbed the tears off her cheek. "I'm sorry I'm late. Demon kept me busy," she explained briefly as she started to figure a way to untangle the chains.

He shook his head. "No, it was a good thing you came late. You wouldn't have stood a chance against Sebastian, and I wouldn't be able to talk to you now."

"If I hadn't come any sooner, you might have bled to death," she said. "Damn it. What on earth are these things? Why are they so intricate?"

He nudged her with his head to stop her from what she was doing. "It's no use. It's Angel Chains. The slightest touch of it will shock me."

"Oh," she said, carefully releasing the chains, "and you didn't stop me when I kissed you. I could've hurt you."

"The pain would've been worth it," he said then sighed. "Sebastian's planned everything too well. You have to leave, Clary."

"No, and if I do, it'll be no use anyway. I'll just come looking for you again."

"But with better aid," he replied. "Please, Clary."

She shook her head. "I won't go anywhere without you."

"So what? You're going to carry me? Like that's possible."

"I can use a strengthening rune."

"Then what? We get out safely, and I'll still be stuck in these chains. And he'll find us again anyway. He knows, Clary. I hate to admit it, but he knows our every move. Even the Clave can't protect us."

She cupped his face with her hands and leveled her head with his, so their eyes met. "I know," she said, "that's why I can't leave you. So what if I come with better aid? Sebastian will always be a step ahead of us." She smirked. "Besides, he claims he loves me. Maybe I can use that to kill him."

He was about to protest, but she stopped him with a kiss. He caught his breath. "Fine," he said, rolling his eyes. "It's not like this is the first time you won't listen to me." He shifted his eyes from Clary to Sebastian. "He's going to come around soon," he said and looked at her again. "Clary, do you remember that rune I taught you just recently."

She nodded carefully. "_Eternal Sleep_."

He smiled. "So you do listen to me when I teach and not just stare at my six-pack," he said. Before she could react, he continued, "Do me a favor, and save me from this torture. I have a feeling Sebastian intends to use me in worse ways we can't imagine."

Her eyes widened. "You want me to mark you? But Jace, you said ordinary Nephilims can't undo them."

"Exactly. So Sebastian can't do anything to me while I'm asleep. It's basically just like the state your mother was in except Shadowhunter style." He saw that she hesitated, and he leaned her forehead against hers. "Don't worry. We might not be able to talk, but we'll still see each other in our dreams. We will. I mean, come on, name one person who's met me and hasn't dreamt to be with me."

She rolled her eyes. "Fine," she muttered under her breath and gave him another kiss, but this time, only on the forehead. She felt him suck his breath, expecting the kiss to be on the lips. He shuddered when she touched his lips with her fingers, and she smirked. "That," she whispered, "is to motivate you to rise sooner. No real kisses until you're back awake.

"Sweet dreams."

He closed his eyes as she took her stele out and began marking him. As soon as she was done, she gave him one last look. He looked peaceful.

She went towards where Sebastian lay and knelt down. He was breathing evenly, quite peacefully like Jace, but there was an ugly burn on his face. Sighing, she grabbed his arm, rolled up his sleeve, and marked him with _Iratze_ to speed up his recovery.

Dropping her stele, she sat beside him and waited.

For a moment, her eyes lingered on him, so she could study him. His clothes told her he came from someplace cold. He wore a handsome-looking black trench coat that emphasised his slim but muscular built. She had to admit it wasn't hard for him to look gorgeous in it with skinny dark jeans that made his long, slender legs look even longer. Anyone would have mistaken him for a model. Everything about him looked neat, and even his face looked so pure, nobody would've thought he was a monster.

Her gaze broke off when she saw him move.

"Clarissa," Sebastian choked as he carefully sat up. He rubbed the mark the burn left on his face before he looked up at her. She said nothing in return.

It was an odd reunion for the both of them. He scanned her with a long, hard gaze. Clary looked at him with pure hatred, but when her green eyes met his dark ones, there was a sense of familiarity once more.

She looked away, and he smiled.

"I see you have grown," he said. She trembled slightly, fearing he would touch her, but he didn't.

Instead, he stood up. "Tell me," he said, offering his hand, which she refused, and he simply smirked and folded his arms. "Did you have a good time with Stupidas? I deliberately sent him to you, so you wouldn't have a hard time."

"He was easier to destroy than the glamour."

"Ah yes, the glamour. I'm impressed you were able to unveil it given your..." He paused for a moment and turned his head toward Jace. "Distractive training."

She snorted. "You'd be surprised at how strict Jace actually is," she said, half-hoping she would piss him off even just a bit.

He kept his face cool and indifferent. "You've put him to eternal unconsciousness," he said, as he walked near Jace and touched the chains that held him. "Clever. So now, he won't feel a single thing physically. But now I also won't feel bad hurting him when I need to."

"Don't touch him."

He chuckled. "Is that a warning, dear sister?"

"I am not your sister."

"Our genes say otherwise," he replied. "We are family, Clarissa, whether you like it or not. It is a fact you cannot change."

"Family does not necessarily entail blood relationships. Family is what you call the people you love. You, Sebastian dear, are unfortunately not one of them."

Sebastian looked unaffected. "That does not mean it cannot be changed."

She was taken aback. "I can't believe you would even think that after all you've done..."

"You despise me for what I did. I understand."

"Oh despise is not enough to describe what I feel for you."

He shrugged. "Hit me."

"What?"

"Hit me if that will help decrease the hatred I've caused you. I promise I won't strike back on you... or Jace."

"I don't understand."

He sighed. "Clarissa, you are my little sister. I have Jace, my adoptive little brother whom you call the love of your life, in chains that only I can undo. We are family. You probably know by now that we will spend the rest of our lives tied to one another whether you like it or not. It will be difficult to live in hatred, so I'm giving you a chance to hit me right now. Hit me with all your might, Clarissa, because you shall never come across this opportunity ever again. We have many far more important things we must do. Besides, you know you want to."

She paced forward towards him and grabbed him by the collar. He let her pull him briskly near her as she held her fist up, prepared to hit him hard in the face. But she hesitated. "No," she said. "If I hit you, it would just please you. I don't want that."

He looked at her lightly and leaned forward to her ear and whispered, "I tell you this now because I know you will hate me even more for it, and when you do, you will want to hit me. But hitting me in the future won't be as easy as now since I won't let you do as you please." He touched her cheek with one hand and smirked, his eyes shining brightly before he continued, "I have been told that my actions were disgusting, but I do not regret attempting to rape you, dear sister. In fact, every night I curse myself for failing. I want you, Clary, because you belong to me, and I to you. You are mine no matter how much you think you love that Angel bastard."

It was enough to provoke her, and she hit him.

As she buried her fist in his warm cheek, a great whiteness suddenly loomed over her. It was a light that was neither majestic nor deadly; it was just… white.

She lost consciousness, falling into the arms of Sebastian, whose face looked calm and serene.

He smiled as he planted his lips softly on her head and carried her up gently in his arms. "We're going to have so much fun, little sister," he whispered in her ear. "And this time, you'll learn to love me."

* * *

_First of all, I'd like to reiterate that there would be no incest. Sebastian says he belongs to Clary, and I'd simply like to experiment on whether or not it will be true, if his feelings for her were… acceptable. I never really saw him as much of a brother to Clary to begin with, seeing that Clary was initially even physically attracted to him. So, yes, I intend to make some twists on Sebastian's background along the way to make things possible._

_Secondly, I thought of this because I honestly see goodness in Sebastian. There's just something about him, something that really makes him no different from Jace, yet sadly, he is so badly received because of the damages he didn't ask for and he can't help but embrace. So, sometimes, I can't help but feel that beneath his wickedness, some of the emotions he feels are genuine; not crafted for manipulation. Perhaps if he was just given a chance... Well, that's just my opinion. _

_Just wanted to point these out to give you a heads up on where this story might possibly go and since my friends think I'm crazy and maybe secretly pure evil for having Sebastian as one of my favorite characters—next to Magnus Bane and Jace of course. ;)_

_**Thank you for your time, and please, **_**please**_** do let me know if you're interested to see how I plan to make Sebastian truly a good part of Clary's life (again, whether romantically or platonically, we'll find out here). Just any sign-a comment, follow, PM, anything-would truly inspire me to continue this especially since this is my first ever Mortal Instruments fan fic, and it's already well-thought of. It's just that I'd like to know whether this plot I've come up with would be accepted by you who have read this far. :)**_


End file.
